Alongside pro-war cheerleaders like Christopher Hitchens, were those who expressed honest doubt and ambiguity, such as Ian McEwan.

Thousands of people march along the Embankment towards Hyde Park as they participate in an antiwar protest march February 15, 2003 in London, England. Photograph: Getty Images.

No event since the 1984 miners’ strike has divided the left more than the Iraq war. Friendships were ended, political reputations were destroyed and antagonists accused each other of betrayal. Few were more stridently supportive of the US-led invasion of what was once Mesopotamia than Christopher Hitchens. Because he was such a good writer and such a powerful rhetorician, and because he had disciples and followers and inspired lesser imitators, his influence became all pervasive during the run-up to the war and in its long, desperate aftermath. For a time, the “pro-war left” had momentum and even its own “Euston Manifesto” – and Hitchens was cheerleader-in-chief.

One of the best pieces I read on the eve of the invasion was by Ian McEwan, on the openDemocracy website, an anguished expression of honest doubt and ambiguity. “The hawks,” he wrote, “have my head, the doves my heart. At a push I count myself – just – in the camp of the latter. And yet my ambi - valence remains . . . One can only hope now for the best outcome: that the regime, like all dictatorships, rootless in the affections of its people, will crumble like a rotten tooth . . . and that the US, in the flush of victory, will find in its oilman’s heart the energy and optimism to begin to address the Palestinian issue. These are fragile hopes. As things stand, it is easier to conceive of innumerable darker possibilities.”

In the event, darkness prevailed as the state of Iraq, an artificial post-colonial construct held together by one man’s brutality, fragmented into sectarianism, suicide slaughter and chaos. Today, McEwan is among those liberal writers and intellectuals – one includes here the New Yorker journalists David Remnick and George Packer – who publicly regret supporting the war.

The only major writer I can think of who made the journey in reverse is the Nobel laureate Mario Vargas Llosa. He opposed the invasion but then, several years later, following a visit to Iraq, wrote unequivocally in support of it: “All the suffering that the armed intervention has inflicted on the Iraqi people is small compared to the horror they suffered under Saddam Hussein.”

Saddam may be long dead, but the suffering goes on and surely nothing short of partition can ease the conflict between Kurds, Shias and Sunnis as the blood-dimmed tide washes over this desert land.

This is an extract from Jason Cowley's First Thoughts column, which appears in this week's issue of the New Statesman